"Carbon monoxide level when we got on the scene was relatively high," Dan Pfannenstiel, assistant chief of the West Metro Fire Protection District, said. "The fire fighters had to go on air in order to go and make sure everybody was out."

The issue happened in the 9500 block of Hialeah Place in Jefferson County in a single-family home around 11 a.m.

The Finnegans, their children, and a neighbor were among the 10 people taken to St. Anthony Hospital in Lakewood. They spent six hours in the emergency room where doctors can conduct hyperbaric oxygen therapy.

They were released around 6:00 p.m. Tuesday night. All patients are expected to fully recover.

Over the years, Colorado has seen various carbon monoxide poisoning situations. From college dormitories to ice arenas to homes. The worst situation was in 2008 when the Lofren family, two parents and two children, died while staying at a home in Aspen.

Their deaths led to the passage of a law requiring carbon monoxide alarms in all new residential structures or remodels.

In the Finnegan home, Pfannenstiel says there were no working carbon-monoxide detectors in the home at the time of the leak.

"Great takeaway message is to make sure everybody has a functioning and properly located carbon monoxide detector in their structures," Pfannenstiel said.

It is unknown at this time how the leak happened. Xcel energy inspected the home and its gas furnance and hot water heater. An Xcel spokesman says the source of the leak has yet to be found.

A West Metro Fire Protection District official, Gary Armstrong, says an HVAC expert will be called in to inspect the ventilation system before the family is allowed to return home.

"This could've had an entirely different outcome had this happened in the middle of the night," Pfannenstiel said.